Variable Valve Operating Apparatus

ABSTRACT

The present invention relates to a variable valve operating apparatus having a switching mechanism for switching between a dual valve variable control mode and a single valve variable control mode, and enhances the durability of the switching mechanism. 
     In an idle state prevailing before a vehicle starts moving, the operating state of an internal combustion engine is in a single valve small lift region (point A). In this instance, the single valve variable control mode prevails. After the vehicle starts moving, the operating state changes from point A through point B to point C and switches to a dual valve great lift region. Subsequently, when an accelerator pedal is released with a clutch disengaged for upshifting, the operating state reverts to point A in the single valve small lift region. In the above situation, as the operating state remains in the dual valve great lift region for a short period of time, a switch to the dual valve variable control mode does not constitute a considerable advantage. Therefore, the switch to the dual valve variable control mode is prohibited when the operating state changes from point B to point C.

TECHNICAL FIELD

The present invention relates to a variable valve operating apparatus,and more particularly to a variable valve operating apparatus that iscapable of mechanically changing a valve opening amount.

BACKGROUND ART

It is known that a conventional variable valve operating apparatusdescribed, for instance, in Patent Document 1 mechanically changes thelift amount and operating angle of a valve in accordance with theoperating state of an internal combustion engine.

In the variable valve operating apparatus described in Patent Document1, two rotary cams are installed over a camshaft. Two intake valves areprovided for a single cylinder. A first intake valve is opened andclosed by a first rotary cam. A second intake valve is opened and closedby a second rotary cam. A variable valve transmission mechanism, whichincludes a four-joint link mechanism, is positioned between the firstrotary cam and the first intake valve and between the second rotary camand the second intake valve.

The four-joint link mechanism of the above variable valve operatingapparatus includes an input arm, which has an input section that abutsagainst the rotary cams; a transmission arm, which is swingably coupledto the input arm; a swing arm, which is swingably coupled to thetransmission arm, can swing on a rotation control shaft, and receivesdriving force from the rotary cams and transmits it to an output sectionthat opens/closes the intake valves; and a control arm, which rotates onthe rotation control shaft and is swingably coupled to the input arm.The operating angles and lift amounts of the intake valves can bemechanically changed by controlling the posture of the four-joint linkmechanism to change the positional relationship between the rotary camsand input section.

Further, the above variable valve operating apparatus includes acoupling mechanism for coupling a first link mechanism, which is afour-joint link mechanism related to the first intake valve, to a secondlink mechanism, which is a four-joint link mechanism related to thesecond intake valve, and a mechanism for keeping the posture of thesecond link mechanism at the time of uncoupling so as to maximize theoperating angle of the second intake valve. The coupling mechanismincludes a through-hole, which is made in the control arm of eachfour-joint link mechanism, and a coupling pin, which is to be insertedinto the through-hole. The mechanism for keeping the posture of thesecond link mechanism at the time of uncoupling includes a through-holemade in a fixed plate, a through-hole made in a second control arm (thecontrol arm for the second link mechanism), and the aforementionedcoupling pin.

The coupling pin is constantly inserted in the through-hole in thesecond control arm, and can move toward a first control arm, which isthe control arm for the first link mechanism, or toward the fixed platewhile being inserted in the through-hole in the second control arm. Whenthe coupling pin moves toward the first control arm and goes into thethrough-hole in the first control arm, the second control arm is coupledto the first control arm via the coupling pin. When the control arms arecoupled together, the first and second link mechanisms maintain the sameposture. In this instance, control is exercised so that the valveopening amounts of the first and second valves are equal.

When, on the contrary, the coupling pin moves toward the fixed plate andgoes into the through-hole in the fixed plate, the second control arm iscoupled to the fixed plate via the coupling pin. When the second controlarm is coupled to the fixed plate, the second link mechanism maintains apredetermined posture. In this instance, when the posture of the firstlink mechanism is controlled to change the positional relationshipbetween the rotary cams and input section, only the valve opening amountof the first valve can be mechanically changed while the valve openingamount of the second valve is fixed.

In other words, the above variable valve operating apparatus can selecta mode in which the first and second intake valves have the same valveopening amount or a mode in which the first and second intake valvesdiffer in the valve opening amount. The valve opening amounts,particularly the lift amounts, of the first and second intake valves canthen be made different from each other. Since this gives rise todifferent intake flow rates, a swirl flow can be created within acombustion chamber to assure increased combustion stability in thecombustion chamber.

Patent Document 1: Japanese Patent Laid-open No. 2004-100555

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

As implied above, the above variable valve operating apparatus canchoose between a dual valve variable control mode in which the valveopening amounts of the first and second intake valves are varied and asingle valve variable control mode in which only the valve openingamount of the first intake valve is varied with the valve opening amountof the second intake valve fixed. When switching from the dual valvevariable control mode to the single valve variable control moved, it isnecessary to perform two operations, that is, extract the coupling pinfrom the pin hole in the first control arm and insert the coupling pininto the pin hole in the fixed plate. When, on the other hand, switchingfrom the single valve variable control mode to the dual valve variablecontrol mode, it is necessary to perform two operations, that is,extract the coupling pin from the pin hole in the fixed plate and insertthe coupling pin into the pin hole in the first control arm.

The internal combustion engine described above switches between the dualand single valve variable control modes in accordance with the operatingstate. In a low engine speed/low load region, for instance, the singlevalve variable control mode is selected because it is demanded that aswirl be created within a cylinder to provide combustion improvement. Ina high engine speed/high load region, on the other hand, the dual valvevariable control mode is selected because it is demanded that a largeamount of air be taken in. More specifically, a control device for theinternal combustion engine stores rules for dividing an operating regioninto a dual valve variable control region, for which the dual valvevariable control mode should be selected, and a single valve variablecontrol region, for which the single valve variable control mode shouldbe selected. When the operating state of the internal combustion engineshifts from one region to another, the control device switches betweenthe dual and single valve variable control modes accordingly.

However, if the control device frequently switches between the dual andsingle valve variable control modes, it is likely that the durability ofa switching mechanism will be adversely affected due to premature wearof the aforementioned coupling pin and pin hole, which constitute theswitching mechanism. Further, such frequent switching might result inswitching failure. If switching failure should occur, proper valveopening characteristics will not be obtained. This results in thefailure to obtain expected fuel efficiency and driveability.

The present invention has been made in view of the above circumstances.An object of the present invention is to provide a variable valveoperating apparatus that includes a switching mechanism for switchingbetween the dual and single valve variable control modes and improvesthe durability of the switching mechanism.

ADVANTAGES OF THE INVENTION Means for Solving the Problem

First aspect of the present invention is a variable valve operatingapparatus comprising:

a valve mechanism having a switching mechanism for switching between adual valve variable control mode in which the valve opening amounts of afirst valve and a second valve, which are provided for the same cylinderand of the same type, are varied continuously or in multiple steps and asingle valve variable control mode in which the valve opening amount ofthe first valve is varied continuously or in multiple steps with thevalve opening amount of the second valve fixed;

storage means for storing rules for dividing an operating region of aninternal combustion engine into a dual valve variable control region,for which the dual valve variable control mode should be selected, and asingle valve variable control region, for which the single valvevariable control mode should be selected;

normal control means for causing the switching mechanism to perform aswitching operation in accordance with the rules;

condition judgment means for judging, when the operating state of theinternal combustion engine switches from the dual valve variable controlregion to the single valve variable control region or vice versa,whether a predefined condition is established for anticipating that theoperating state will revert to the previous region within a short periodof time; and

disable means for disabling the switching operation when the predefinedcondition is established.

Second aspect of the present invention is the variable valve operatingapparatus according to the first aspect, wherein the predefinedcondition denotes a condition where a predetermined period of time hasnot elapsed since a gear shift by a transmission positioned between theinternal combustion engine and vehicle driving wheels.

Third aspect of the present invention is the variable valve operatingapparatus according to the first aspect, wherein the predefinedcondition denotes a condition where a transmission positioned betweenthe internal combustion engine and vehicle driving wheels is shifted toneutral or park.

Fourth aspect of the present invention is the variable valve operatingapparatus according to any one of the first to the third aspects,further comprising:

enable means for enabling the switching operation if the operating stateof the internal combustion engine does not revert to a previous regionwithin a predetermined period of time after a switch from the dual valvevariable control region to the single valve variable control region orvice versa.

Fifth aspect of the present invention is the variable valve operatingapparatus according to any one of the first to the fourth aspects,further comprising:

measurement means for measuring the number of times the switchingoperation was disabled or the cumulative time during which the switchingoperation was disabled; and

permission means which, when a predetermined value is exceeded by thenumber of times the switching operation was disabled or the cumulativetime during which the switching operation was disabled, permits theswitching mechanism to perform a switching operation no matter whetherthe predefined condition is established.

Sixth aspect of the present invention is the variable valve operatingapparatus according to any one of the first to the fifth aspect, furthercomprising:

valve opening amount limitation means for limiting a target valveopening amount when the switching operation is disabled by the disablemeans.

Seventh aspect of the present invention is the variable valve operatingapparatus according to the sixth aspect,

wherein the valve mechanism includes a main cam, which drives both thefirst valve and the second valve in the dual valve variable control modeand drives only the first valve in the single valve variable controlmode; and a sub-cam, which drives the second valve in the single valvevariable control mode; and

wherein the valve opening amount limitation means limits the targetvalve opening amount so as to keep the sub-cam from leaving a matingmember for the sub-cam when the disable means disables a switch from thesingle valve variable control mode to the dual valve variable controlmode to maintain the single valve variable control mode.

EFFECTS OF THE INVENTION

According to the first aspect of the present invention, the switchingmechanism can switch between the dual valve variable control mode andsingle valve variable control mode. This switching operation isperformed in accordance with rules for dividing the operating region ofthe internal combustion engine into the dual valve variable controlregion and single valve variable control region depending on theoperating state of the internal combustion engine. However, theswitching operation is disabled if, when the operating state switchesfrom the dual valve variable control region to the single valve variablecontrol region or vice versa, a predefined condition is established foranticipating that the operating state will revert to the previous regionwithin a short period of time. Therefore, the first aspect of thepresent invention makes it possible to reduce the frequency of switchingoperation by avoiding unnecessary switching operations. Consequently,the durability of the switching mechanism can be increased by avoidingundue wear and scratching of the switching mechanism. Further, thepossibility of switching failure can be reduced to constantly implementvalve opening characteristics according to the operating state andproperly obtain satisfactory fuel efficiency characteristics, exhaustcharacteristics, and driveability.

According to the second aspect of the present invention, it is possibleto absolutely avoid an unnecessary switching operation that is likely totake place immediately after gear shifting by the transmission.Therefore, the frequency of switching operation can be reduced while thevehicle is moving.

According to the third aspect of the present invention, it is possibleto absolutely avoid an unnecessary switching operation during a freeacceleration (so-called racing) operation, which is performed while thetransmission is in neutral or parking position. Therefore, the frequencyof switching operation can be reduced during free acceleration.

If the operating state of the internal combustion engine does not revertto a previous region within a short period of time after it is changedfrom the dual valve variable control region to the single valve variablecontrol region or vice versa, the fourth aspect of the present inventioncan enable the switching operation and perform the switching operation.Therefore, if the switching operation is actually needed in a situationwhere it is assumed that no switching operation is needed, the switchingoperation can be performed to implement preferred valve openingcharacteristics.

When a predetermined value is exceeded by the number of times theswitching operation was disabled or the cumulative time during which theswitching operation was disabled, the fifth aspect of the presentinvention can perform the switching operation even in a situation wherea condition for anticipating that the switching operation is unnecessaryis established. Therefore, the switching operation can be performed inany situation with frequency required for maintaining the function ofthe switching mechanism. This makes it possible to avoid problems, forinstance, by preventing the switching mechanism from binding due tolong-term inactivity.

When the operation for switching between the dual valve variable controlmode and single valve variable control mode is disabled, the sixthaspect of the present invention can limit the target valve openingamount. This makes it possible to absolutely avoid noise and otherproblems that may arise when the switching operation is disabled.

When the operation for switching from the single valve variable controlmode to the dual valve variable control mode is disabled to maintain thesingle valve variable control mode in a situation where the valvemechanism includes the main cam, which drives both the first valve andthe second valve in the dual valve variable control mode and drives onlythe first valve in the single valve variable control mode, and thesub-cam, which drives the second valve in the single valve variablecontrol mode, the seventh aspect of the present invention can limit thetarget valve opening amount so that the sub-cam does not leave itsmating member. Since this feature absolutely prevents the sub-cam fromleaving the mating member and coming back into contact (colliding) withit, it is possible to absolutely avoid noise generation from collisionand prevent the surfaces of the sub-cam and its mating member from beingdamaged.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the configuration of a system that includes avariable valve operating apparatus according to a first embodiment ofthe present invention.

FIG. 2 is a perspective view illustrating the configuration of a valvemechanism included in the variable valve operating apparatus accordingto the first embodiment of the present invention.

FIG. 3 illustrates the configuration of a variable valve mechanismincluded in the valve mechanism shown in FIG. 2.

FIG. 4 is an exploded perspective view illustrating variable valvemechanisms and fixed valve mechanism shown in FIG. 2.

FIG. 5 is a schematic diagram illustrating the configuration of ahydraulic system for operating a switching pin.

FIG. 6 shows a map for switching between a dual valve variable controlmode and a single valve variable control mode.

FIG. 7 shows a map for switching between the dual valve variable controlmode and the single valve variable control mode.

FIG. 8 is a flowchart illustrating a routine that is executed by thefirst embodiment of the present invention.

FIG. 9 is a flowchart illustrating a routine that is executed by asecond embodiment of the present invention.

FIG. 10 is a flowchart illustrating a routine that is executed by athird embodiment of the present invention.

FIG. 11 shows valve lift curves of a first intake valve and a secondintake valve.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment SystemConfiguration

FIG. 1 illustrates the configuration of a system that includes avariable valve operating apparatus according to a first embodiment ofthe present invention. The system shown according to the firstembodiment includes an internal combustion engine 1, which is mounted ina vehicle as a driving source. The internal combustion engine 1 includesa plurality of cylinders 2. FIG. 1 shows only one of the plurality ofcylinders 2.

The internal combustion engine 1 also includes a cylinder block 4. Thecylinder block 4 houses a piston 3 within a cylinder. The piston 3 isconnected to a crankshaft 5 via a connecting rod. A crank angle sensor 6is installed near the crankshaft 5. The crank angle sensor 6 isconfigured to detect the rotation angle of the crankshaft 5.

A cylinder head 8 is attached to the top of the cylinder block 4. Acombustion chamber 10 is formed by the space between the upper surfaceof the piston 3 and the cylinder head 8. The cylinder head 8 is providedwith an ignition plug 11, which ignites an air-fuel mixture in thecombustion chamber 10.

The cylinder head 8 has an intake port 12 that communicates with thecombustion chamber 10. The joint between the intake port 12 andcombustion chamber 10 is provided with an intake valve 14. A valvemechanism 18 is installed between the intake valve 14 and an intake cam16 on an intake camshaft 15. The valve mechanism 18 will be described indetail later.

The intake port 12 is connected to an intake path 19. An injector 20 isinstalled near the intake port 12 to inject fuel into the intake port12. A surge tank 21 is positioned in the middle of the intake path 19.

A throttle valve 22 is installed upstream of the surge tank 21. Thethrottle valve 22 is an electronically-controlled valve that is drivenby a throttle motor 23. The throttle valve 22 is driven in accordancewith an accelerator opening AA, which is detected by an acceleratoropening sensor 24. A throttle opening sensor 25 is installed near thethrottle valve 22. The throttle opening sensor 25 is configured todetect a throttle opening TA. An air flow meter 26 is installed upstreamof the throttle valve 22. The air flow meter 26 is configured to detectan intake air amount Ga. An air cleaner 27 is installed upstream of theair flow meter 26.

Further, the cylinder head 8 has an exhaust port 28 that communicateswith the combustion chamber 10. The joint between the exhaust port 28and combustion chamber 10 is provided with an exhaust valve 29. Theexhaust port 28 is connected to an exhaust path 30. An air-fuel ratiosensor 31 is installed in the exhaust path 30 to detect an exhaustair-fuel ratio.

The system according to the present embodiment also includes an ECU(Electronic Control Unit) 60 as a control device. The output end of theECU 60 is connected, for instance, to a discharge valve 84 (see FIG. 5),which will be described later, in addition to the ignition plug 11,valve mechanism 18, injector 20, and throttle motor 23. The input end ofthe ECU 60 is connected, for instance, to the crank angle sensor 6,throttle opening sensor 25, accelerator opening sensor 24, air flowmeter 26, and air-fuel ratio sensor 31. In accordance with outputsgenerated by the sensors, the ECU 60 exercises control over the entireinternal combustion engine such as fuel injection control and ignitiontiming control.

A transmission (not shown) is positioned between the internal combustionengine 1 and driving wheels of the vehicle. The ECU 60 is also connectedto a shift position sensor 62, which detects the position to which thetransmission is shifted. The transmission may be of either a manual typeor an automatic type.

[Configuration of Variable Valve Train]

FIG. 2 is a perspective view illustrating the configuration of the valvemechanism 18 included in the variable valve operating apparatusaccording to the present embodiment.

As shown in FIG. 2, the intake camshaft 15 has two intake cams (a firstintake cam 16 and a second intake cam 17) for each cylinder. Two intakevalves (a first intake valve 14L and a second intake valve 14R) arepositioned so that the first intake valve 14L and the second intakevalve 14R are left-right symmetrical with respect to the first intakecam 16. Variable valve mechanisms 40L, 40R, which coordinate the liftingmotions of the intake valves 14L, 14R with the rotary motion of thefirst intake cam 16, are respectively positioned between the firstintake cam 16 and the intake valves 14L, 14R. Meanwhile, the secondintake cam 17 is positioned so that the second intake valve 14R issandwiched between the second intake cam 17 and the first intake cam 16.A fixed valve mechanism 70 is positioned between the second intake cam17 and the second intake valve 14R to coordinate the lifting motion ofthe second intake valve 14R with the rotary motion of the second intakecam 17. The valve mechanism 18 is configured to select either thevariable valve mechanism 40R or the fixed valve mechanism 70 as acoordination destination for the lifting motion of the second intakevalve 14R.

(1) Detailed Configuration of Variable Valve Mechanism

FIG. 3 illustrates the configuration of a variable valve mechanism 40 inthe valve mechanism 18 shown in FIG. 2. More specifically, FIG. 3 showsthe variable valve mechanism 40 as viewed in the axial direction of theintake camshaft 15. Since the left- and right-hand variable valvemechanisms 40L, 40R are basically symmetrical with respect to the firstintake cam 16, their configuration will be described withoutdistinguishing between the left- and right-hand variable valvemechanisms 40L, 40R. In this document and accompanying drawings, theterm “variable valve mechanism 40” is used when there is no need todistinguish between the left- and right-hand variable valve mechanisms40L, 40R. Similarly, the symbols L and R, which respectively indicateleft- and right-hand parts, are not attached to the names of thecomponent parts of the variable valve mechanisms 40L, 40R, the intakevalves 14L, 14R, and other symmetrically arranged parts except when itis necessary to distinguish between them.

As shown in FIG. 3, the valve mechanism 18 includes a rocker arm 35 thatpresses the intake valve 14 in the opening direction. The variable valvemechanism 40 is positioned between the first intake cam 16 and rockerarm 35. The variable valve mechanism 40 is configured to continuouslyvary the coordination between the rotary motion of the first intake cam16 and the swing motion of the rocker arm 35.

The variable valve mechanism 40 includes a control shaft 41 that ispositioned in parallel with the intake camshaft 15. A control arm 42 isfastened to the control shaft 41 with a bolt 43. A part of the controlarm 42 projects in the radial direction of the control shaft 41. Anintermediate arm 44 is mounted on the projection of the control arm 42with a pin 45. The pin 45 is positioned eccentrically relative to thecenter of the control shaft 41. Therefore, the intermediate arm 44swings on the pin 45.

A swing cam arm 50 is swingably supported by the control shaft 41. Theswing cam arm 50 has a slide surface 50 a, which faces the first intakecam 16. The slide surface 50 a is formed so as to come into contact witha second roller 53. The slide surface 50 a is curved so that itsdistance to the first intake cam 16 gradually decreases when the secondroller 53 moves from the leading end of the swing cam arm 50 toward theaxial center of the control shaft 41. The swing cam arm 50 also has aswing cam surface 51, which is positioned opposite the slide surface 50a. The swing cam surface 51 includes a nonoperating surface 51 a and anoperating surface 51 b. The nonoperating surface 51 a is formed so thatits distance from the swing center of the swing cam arm 50 is fixed. Theoperating surface 51 b is formed so that its distance from the axialcenter of the control shaft 41 increases with an increase in thedistance to the nonoperating surface 51 a.

A first roller 52 and the second roller 53 are positioned between theslide surface 50 a and the circumferential surface of the first intakecam 16. More specifically, the first roller 52 is positioned so as tocome into contact with the circumferential surface of the first intakecam 16, whereas the second roller 53 is positioned so as to come intocontact with the slide surface 50 a of the swing cam arm 50. The firstand second rollers 52, 53 are both rotatably supported by a couplingshaft 54 that is fastened to the leading end of the intermediate arm 44.Since the intermediate arm 44 swings on the pin 45, these rollers 52, 53swing along the slide surface 50 a and the circumferential surface ofthe first intake cam 16 while maintaining a fixed distance from the pin45.

Further, a spring seat 50 b is formed on the swing cam arm 50. One endof a lost motion spring 38 is engaged with the spring seat 50 b. Theother end of the lost motion spring 38 is fastened to a stationary partof the internal combustion engine. The lost motion spring 38 is acompression spring. The force received from the lost motion spring 38presses the slide surface 50 a of the swing cam arm 50 against thesecond roller 53 and the first roller 52 against the first intake cam16. This positions the first and second rollers 52, 53 so that they aresandwiched between the slide surface 50 a and the circumferentialsurface of the first intake cam 16.

The aforementioned rocker arm 35 is positioned below the swing cam arm50. A rocker roller 36 is attached to the rocker arm 35 so that therocker roller 36 faces the swing cam surface 51. The rocker roller 36 isrotatably mounted on the middle part of the rocker arm 35. One end ofthe rocker arm 35 abuts against a valve shaft 14 a of the valve 14, andthe other end of the rocker arm 35 is rotatably supported by a hydrauliclash adjuster 37. When a lifting operation is conducted, a valve spring(not shown) pushes the valve shaft 14 a in a closing direction, that is,in a direction of pushing up the rocker arm 35. The rocker roller 36 ispressed against the swing cam surface 51 of the swing cam arm 50 by theforce of the valve spring and by the hydraulic lash adjuster 37.

According to the configuration of the variable valve mechanism 40described above, the pushing force of the first intake cam 16 istransmitted to the slide surface 50 a via the first and second rollers52, 53 as the first intake cam 16 rotates. When this moves the contactbetween the swing cam surface 51 and rocker roller 36 from thenonoperating surface 51 a to the operating surface 51 b, the rocker arm35 is pushed downward to open the valve 14.

Further, when the rotational position of the control shaft 41 changes,the configuration of the variable valve mechanism 40 changes theposition of the second roller 53 on the slide surface 50 a, therebychanging the swing range of the swing cam arm 50 for lifting motion.More specifically, when the control shaft 41 rotates counterclockwise inFIG. 3, the position of the second roller 53 on the slide surface 50 amoves toward the leading end of the swing cam arm 50. The rotation angleof the swing cam arm 50 that is required between the instant at whichthe swing cam arm 50 starts a swing motion upon receipt of pushing forcefrom the first intake cam 16 and the instant at which the rocker arm 35actually begins to be pushed then increases as the control shaft 41rotates counterclockwise in FIG. 3. In other words, the operating angleand lift amount of the valve 14 can be decreased by rotating the controlshaft 41 counterclockwise in FIG. 3. On the contrary, clockwise rotationof the control shaft 41 increases the operating angle and lift amount ofthe valve 14.

As described above, the variable valve mechanism 40 according to thepresent embodiment varies both the operating angle and lift amount ofthe valve 14. In this document, the operating angle and lift amount arecollectively referred to as a “valve opening amount.” It should benoted, however, that the variable valve mechanism according to thepresent invention may alternatively be configured to vary either theoperating angle or the lift amount.

(2) Detailed Configuration of Fixed Valve Mechanism

The configuration of the fixed valve mechanism 70 will now be describedin detail with reference to FIGS. 2 and 4. FIG. 4 is an explodedperspective view illustrating the variable valve mechanism 40 and fixedvalve mechanism 70 shown in FIG. 2.

As shown in FIG. 2, the fixed valve mechanism 70 is positioned betweenthe second intake cam 17 and the second swing cam arm 50R. The fixedvalve mechanism 70 coordinates the swing motion of the second swing camarm 50R with the rotary motion of the second intake cam 17. The fixedvalve mechanism 70 includes a great lift arm 71, which is driven by thesecond intake cam 17, and an arm coupling mechanism 72 (see FIG. 4),which couples the great lift arm 71 to the second swing cam arm 50R. Thearm coupling mechanism 72 includes a switching pin 74, a hydraulicchamber 75, a pin hole 76, a return spring 77, and a piston 78, whichwill be described later.

The great lift arm 71, which is mounted on the control shaft 41 andpositioned next to the second swing cam arm 50R, can swing independentlyof the second swing cam arm 50R. An input roller 73, which comes intocontact with the circumferential surface of the second intake cam 17, isrotatably supported by the great lift arm 71.

As shown in FIG. 4, a spring seat 71 a is formed on the great lift arm71. As is the case with the aforementioned swing cam arm 50, a lostmotion spring (not shown) is engaged with the spring seat 71 a. Theforce of the lost motion spring presses the input roller 73 against thecircumferential surface of the second intake cam 17.

The great lift arm 71 includes the switching pin 74, which can beinserted into and extracted from the second swing cam arm 50R. The greatlift arm 71 is provided with the hydraulic chamber 75, which has anopening that is positioned toward the second swing cam arm 50R. Theswitching pin 74 is fitted into the hydraulic chamber 75. The hydraulicchamber 75 is connected to a hydraulic system that will be describedlater. When the hydraulic system raises the hydraulic pressure in thehydraulic chamber 75, the resulting hydraulic pressure pushes theswitching pin 74 out of the hydraulic chamber 75 and toward the secondswing cam arm 50R.

Meanwhile, the second swing cam arm 50R is provided with the pin hole76, which has an opening that is positioned toward the great lift arm71. The switching pin 74 and pin hole 76 are equidistant from the centerof the control shaft 41. From bottom to top, items placed in the pinhole 76 are the return spring 77 and the piston 78 that serves as alifter.

FIG. 5 is a schematic diagram illustrating the configuration of thehydraulic system for operating the switching pin 74. As shown in FIG. 5,an oil path 81 is formed in the control shaft 41. The oil path 81 isconnected to the hydraulic chamber 75, a sliding gap between the controlshaft 41 and the great lift arm 71, and a sliding gap between thecontrol shaft 41 and the second swing cam arm 50R. The oil path 81 isalso connected to a pump 82. A discharge path 83 is connected to themiddle of the oil path 81. The discharge path 83 is provided with thedischarge valve 84. Further, an orifice 85 is installed downstream ofthe discharge valve 84 in the discharge path 83.

Lubricating oil pressurized by the pump 82 is supplied to the abovesliding gaps through the oil path 81. Part of the lubricating oilflowing in the oil path 81 is supplied to the hydraulic chamber 75.Therefore, the hydraulic pressure in the hydraulic chamber 75 can beraised. Meanwhile, opening the discharge valve 84 discharges thelubricating oil from the discharge path 83. This lowers the hydraulicpressure in the hydraulic chamber 75. The switching pin 74 can beoperated by controlling the hydraulic pressure in the hydraulic chamber75.

Features of First Embodiment Single Valve Variable Control Mode

The great lift arm 71 constantly swings as it is driven by the secondintake cam 17. However, while the base circle of the second intake cam17 is in contact with the input roller 73, the great lift arm 71 ismomentarily stationary. The second swing cam arm 50R also swings as itis driven by the first intake cam 16. However, while the base circle ofthe first intake cam 16 is in contact with the first roller 52, thesecond swing cam arm 50R is momentarily stationary. The periods duringwhich the great lift arm 71 and the second swing cam arm 50R arestationary overlap with each other. In other words, there is a periodduring which the great lift arm 71 and the second swing cam arm 50R aresimultaneously stationary.

The angle of the second swing cam arm 50R in the above stationary statevaries with the rotational position of the control shaft 41. Therefore,there is a rotational position of the control shaft 41 at which theswitching pin 74 aligns with the pin hole 76 while the great lift arm 71and the second swing cam arm 50R are stationary. This rotationalposition of the control shaft 41 is hereinafter referred to as the “pinswitching position.” In the valve mechanism 18, the pin hole 76 alignswith the switching pin 74 when the rotational position of the controlshaft 41 agrees with the pin switching position. In this state,therefore, the arm coupling mechanism 72 can perform a switchingoperation as described below.

When the pin hole 76 aligns with the switching pin 74, the switching pin74 abuts against the piston 78. If, in this state, the force exerted bythe hydraulic pressure in the hydraulic chamber 75 to push the switchingpin 74 is greater than the force exerted by the return spring 77 to pushthe piston 78, the switching pin 74 enters the pin hole 76 to push thepiston 78 all the way into the pin hole 76. In other words, theswitching pin 74 can be inserted into the pin hole 76 by allowing thehydraulic system to raise the hydraulic pressure in the hydraulicchamber 75. When the switching pin 74 is inserted into the pin hole 76,the second swing cam arm 50R is coupled to the great lift arm 71. Thecoordination destination for the lifting motion of the second intakevalve 14R then changes from the variable valve mechanism 20R to thefixed valve mechanism 70.

In the above instance, the rotary motion of the intake camshaft 15 istransmitted from the second intake cam 17 to the second swing cam arm50R via the great lift arm 71. The valve opening amount of the secondintake valve 14R is mechanically determined by the shapes of the secondintake cam 17, great lift arm 71, and second swing cam arm 50R and thepositional relationship between them. It is constantly fixed aspredetermined (to provide a great lift and large operating angle)irrespective of the rotational position of the control shaft 41.Meanwhile, the first intake cam 16 transmits the rotary motion of thefirst intake cam 16 to the first swing cam arm 50L via the first andsecond rollers 52, 53L. Consequently, the valve opening amount of thefirst intake valve 14L varies with the rotational position of thecontrol shaft 41.

In this document, a state in which the valve opening amount of the firstintake valve 14L varies with the rotational position of the controlshaft 41 while the valve opening amount of the second intake valve 14Rremains large as described above is referred to as the “single valvevariable control mode.” In the single valve variable control mode, it ispossible to provide the second intake valve 14R with a great lift andthe first intake valve 14L with a small lift. This causes the secondintake valve 14R to flow a large amount of air to the cylinder and thefirst intake valve 14L to flow a small amount of air to the cylinder. Asthe air flow rates differ as mentioned above, a swirl flow can becreated within the cylinder. Creating the swirl flow provides combustionimprovement in a low engine speed/low load region.

(Dual Valve Variable Control Mode)

The switching pin 74 can be extracted from the pin hole 76 by loweringthe hydraulic pressure in the hydraulic chamber 75 when the pin hole 76aligns with the switching pin 74. The great lift arm 71 is thenuncoupled from the second swing cam arm 50R. Thus, the coordinationdestination for the lifting motion of the second intake valve 14R can bechanged from the fixed valve mechanism 70 to the variable valvemechanism 20R.

In the above instance, the rotary motion of the camshaft 15 istransmitted from the first intake cam 16 to the slide surfaces 50 a ofthe first and second swing cam arms 50L, 50R via the first and secondrollers 52, 53. Therefore, the valve opening amounts of the first andsecond intake valves 14L, 14R both vary in accordance with the rotationof the control shaft 41. Consequently, the valve opening amounts of thefirst and second intake valves 14L, 14R can be both varied in accordancewith the rotational position of the control shaft 41. In this document,a state in which the valve opening amounts of the first and secondintake valves 14L, 14R are both variable as described above is referredto as the “dual valve variable control mode.”

The ECU 60 switches between the dual valve variable control mode andsingle valve variable control mode in accordance with the operatingstate (more specifically, the engine speed NE and load) of the internalcombustion engine 1. FIG. 6 shows a switching map that is stored in theECU 60 and used for switching between the dual valve variable controlmode and single valve variable control mode. This switching map shows anoperating region of the internal combustion engine 1 by indicating theengine speed NE along the horizontal axis and the load along thevertical axis.

Here, the term “load” denotes an internal combustion engine torque, loadrate, accelerator opening AA, or other index correlating to the load onthe internal combustion engine 1. The ECU 60 can calculate the value ofthe load in accordance with outputs generated from the acceleratoropening sensor 24, air flow meter 26, and the like. Further, the ECU 60can calculate the engine speed NE in accordance with an output generatedfrom the crank angle sensor 6. In this manner, the ECU 60 can determinethe current operating state of the internal combustion engine 1 withreference to the switching map.

In FIG. 6, a switching pin operating line P represents a boundary forswitching between the dual and single valve variable control modes. Twocircles positioned side by side represent the first and second intakevalves 14L, 14R, and the words within the circles indicate whether thevalve opening amount is large or small.

As shown in FIG. 6, a region that is lower in engine speed and lower inload than the switching pin operating line P is a region of the singlevalve variable control mode. In the present embodiment, this region isreferred to as the “single valve small lift region.” The single valvesmall lift region provides a coupled state in which the switching pin 74of the arm coupling mechanism 72 is inserted into the pin hole 76.

On the other hand, a region that is higher in engine speed and higher inload than the switching pin operating line P is a region of the dualvalve variable control mode. In the present embodiment, this region isreferred to as the “dual valve great lift region.” The dual valve greatlift region provides an uncoupled state in which the switching pin 74 ofthe arm coupling mechanism 72 is extracted from the pin hole 76.

The ECU 60 usually switches between the single and dual valve variablecontrol modes in accordance with the switching map described above. Ingeneral, unstable, incomplete combustion is likely to result in a lowengine speed/low load region. However, the present embodiment can createa swirl for combustion improvement by providing the second intake valve14R with a great lift and the first intake valve 14L with a small liftin the single valve small lift region, which corresponds to a low enginespeed/low load region. This makes it possible to reduce fuel consumptionand exhaust emissions. In the dual valve great lift region, whichcorresponds to a high engine speed/high load region, on the other hand,the present embodiment can introduce an adequate amount of air into thecylinder by providing both intake valves 14 with a great lift.

When the operating state of the internal combustion engine 1 changesfrom the single valve small lift region to the dual valve great liftregion, the ECU 60 usually switches to the dual valve variable controlmode by extracting the switching pin 74 from the pin hole 76 withoutdelay. However, it is conceivable that the ECU 60 may revert to thesingle valve small lift region within a short period of time dependingon the situation even when the operating state changes from the singlevalve small lift region to the dual valve great lift region.

The above situation may occur when, for instance, the vehicleaccelerates after it has started moving. Before the vehicle startsmoving, the internal combustion engine 1 is idling as indicated by pointA in FIG. 6. As the vehicle accelerates after starting in first gear,the operating state changes from point A to point B in FIG. 6 and thenfrom point B to point C. Subsequently, an accelerator pedal is releasedwith a clutch disengaged to shift up to second gear. Since this causesthe internal combustion engine 1 to revert to an idling state, theoperating state changes from point C to point A.

Shifting up to third gear and then fourth gear brings about the samechanges as described above. In other words, when the vehicle acceleratesafter it has started moving, the operating state of the internalcombustion engine 1 changes from point A through point B, point C andthen back to point A in FIG. 6 within a relatively short period of time.If, in such an instance, the arm coupling mechanism 72 immediatelyperforms a switching operation in accordance with the switching mapshown in FIG. 6, the switching pin 74 is extracted from the pin hole 76when the operating state changes from point B to point C, and theninserted back into the pin hole 76 when the operating state changes frompoint C to point A. It means that the dual valve variable control modeis maintained for an extremely short period of time when the operatingstate changes from point B through point C to point A. Therefore,switching to the dual valve variable control mode does not constitute aconsiderable advantage. Instead, such switching constitutes asignificant disadvantage. More specifically, frequentinsertion/extraction of the switching pin 74 may cause premature wearand scratching of the switching pin 74 and pin hole 76. Consequently,the present embodiment does not perform a switching operation for theswitching pin 74 in the above situation in consideration of durabilityof the arm coupling mechanism 72.

The above switching operation, which should be avoided, takes place dueto gear shifting by the transmission. Therefore, the present embodimentidentifies and avoids a gear-shift-induced switching operation bytemporarily disabling the switching operation of the arm couplingmechanism 72 during a predetermined period of time after a gear shift bythe transmission.

When the above process is performed, a switching operation that is notabsolutely necessary can be identified and avoided not only when thevehicle accelerates after the start of moving but also in the followingsituation. Points D to K in FIG. 7 indicate operating state changes thatoccur when the vehicle begins to climb a hill during high-speed running.In this situation, the operating state of the internal combustion engine1 changes as described below. When the vehicle begins to run uphill, thevehicle velocity gradually decreases due to grade resistance, therebygradually decreasing the engine speed NE (point D to point E). A driverof the vehicle then shifts down for the purpose of recovering theprevious speed. When the accelerator pedal is released with the clutchdisengaged for downshifting, the internal combustion engine 1 changestoward an idle state (point E to point F). As the accelerator pedal isdepressed after downshifting, the internal combustion engine 1 changestoward a high engine speed/high load state (point F to point G). Asacceleration continues, the engine speed NE increases (point G to pointH). When the vehicle velocity is adequately recovered, the driver shiftsup. When the accelerator pedal is released with the clutch disengagedfor upshifting, the internal combustion engine 1 changes toward an idlestate (point H to point I). After upshifting, the engine speed NE dropsbelow a level prevailing before upshifting (point I to point J). Asteady operation then takes place in the newly selected gear (point J topoint K).

If, in the above situation, the arm coupling mechanism 72 immediatelyperforms a switching operation in accordance with the switching mapshown in FIG. 7, the switching pin 74 is extracted from the pin hole 76when the operating state changes from point F to point G, and after ashort time, the switching pin 74 is inserted back into the pin hole 76when the operating state changes from point H to point I. In this case,too, the dual valve variable control mode persists for an extremelyshort period of time. Therefore, switching to the dual valve variablecontrol mode does not constitute a considerable advantage. Instead, suchswitching constitutes a significant disadvantage because it may causepremature wear of the switching pin 74 and pin hole 76. It means thatthe switching operation in the above case should also be avoided. Thepresent embodiment can refrain from performing the above switchingoperation, which should be avoided, by detecting the execution of a gearshift at point F and temporarily disabling the switching operation ofthe arm coupling mechanism 72 for a predetermined period of time afterdetection.

Details of Process Performed by First Embodiment

FIG. 8 is a flowchart illustrating a routine that the ECU 60 accordingto the present embodiment executes to implement the above functionality.It is assumed that this routine is periodically executed atpredetermined time intervals. First of all, the routine shown in FIG. 8performs step 100 to judge whether a gear shift is performed by thetransmission. The shift position sensor 62 detects whether a gear shiftis performed. If the judgment result obtained in step 100 indicates thatno gear shift is performed, the routine does not perform the followingprocessing steps because it is not necessary to disable the switchingoperation of the arm coupling mechanism 72. In this instance, normalcontrol is continuously exercised so as to immediately switch betweenthe single and dual valve variable control modes in accordance with theswitching map.

If, on the other hand, the judgment result obtained in step 100indicates that a gear shift is performed, step 102 is followed to judgewhether the operating state of the internal combustion engine 1 haschanged from the single valve small lift region to the dual valve greatlift region within a predetermined period of time after the gear shift.The predetermined period of time is based, for instance, on dataobtained by examining the time required for a change from point Bthrough point C to point A in FIG. 6 and a change from point F throughpoint G, point H to point I in FIG. 7, and stored in the ECU 60.

If the judgment result obtained in step 102 does not indicate a changefrom the single valve small lift region to the dual valve great liftregion, it means that the arm coupling mechanism 72 is not instructed toperform a switching operation. In this instance, it is not necessary todisable the switching operation; therefore, the routine continuouslyexercises normal control without performing the following processingsteps.

If, on the other hand, the judgment result obtained in step 102indicates a change from the single valve small lift region to the dualvalve great lift region, step 104 is performed to disable the switchingoperation of the arm coupling mechanism 72. In other words, the routinerefrains from switching to the dual valve variable control mode with theswitching pin 74 left inserted in the pin hole 76 although the operatingstate of the internal combustion engine 1 has switched to the dual valvegreat lift region. When a change from the single valve small region tothe dual valve great lift region is found in step 102, it corresponds toa change from point B to point C in FIG. 6 or a change from point F topoint G in FIG. 7, and it is anticipated that the operating state mayrevert to the single valve small lift region within a short period oftime. Step 104, which is mentioned above, is performed to avoid aswitching operation in such an instance.

Next, the routine shown in FIG. 8 performs step 106 to judge whether apredetermined period of time is reached by the elapsed time since anoperating state change from the single valve small region to the dualvalve great lift region. The present embodiment performs step 104 toavoid a switch to the dual valve variable control mode because itanticipates that the operating state will revert to the single valvesmall lift region within a short period of time. However, the operatingstate may remain in the dual valve great lift region without immediatelyreverting to the single valve small lift region depending on vehicledriving conditions and operations performed by the driver. In such aninstance, a switch to the dual valve variable control mode should bemade to let the internal combustion engine 1 deliver its expectedperformance. Therefore, if the operating state does not revert to thesingle valve small lift region when the predetermined period of time isreached by the elapsed time since a change to the dual valve great liftregion in step 106, the present embodiment terminates the process of theroutine (RETURN) and resumes normal control. When normal controlresumes, a switch to the dual valve variable control mode is made inaccordance with the switching map. It is assumed that the predeterminedperiod of time usually ranges from several seconds to ten-odd secondsalthough its ideal value varies, for instance, with the type of theinternal combustion engine 1 and the use of the vehicle in which theinternal combustion engine 1 is mounted.

Next, the routine shown in FIG. 8 performs step 108 to judge whether theoperating state has changed to a region other than the single valvesmall lift region and dual valve great lift region. The region otherthan the single valve small lift region and dual valve great lift regionis a dual valve variable lift region. In the dual valve variable liftregion, control is exercised in the dual valve variable control mode sothat the lift amounts of both intake valves 14 vary between a mediumlift and a small lift. The dual valve variable lift region is set forthe purpose, for instance, of enhancing the effect of engine brakingwhen the internal combustion engine 1 decelerates. The range of the dualvalve variable lift region is stored in the ECU 60 separately from theswitching map.

If it is found in step 108 that the operating state is changed to thedual valve variable lift region, the routine terminates (RETURN) toresume normal control. When normal control resumes, a switch to the dualvalve variable control mode is made in accordance with predeterminedrules. The dual valve variable lift region can be set as needed, forinstance, for low-load driving, idling, low-temperature startup, and acold climate as well as for deceleration.

Next, the routine shown in FIG. 8 performs step 110 to judge whether theoperating state has changed back from the dual valve great lift regionto the single valve small lift region. In this instance, a switch to thedual valve variable control mode is prohibited by the process performedin step 104 above. If the operating state reverts to the single valvesmall lift region in this instance, no instruction is issued forswitching to the dual valve variable control mode; therefore, there isno need to disable the switching operation. In this situation,therefore, the routine terminates (RETURN) to resume normal control. Ifthe operating state remains in the dual valve great lift region in step110 above, the routine repeats steps 106 and beyond.

If the switching operation of the arm coupling mechanism 72 is notabsolutely necessary, the process described above disables such aswitching operation. This makes it possible to avoid undue wear of thearm coupling mechanism 72 and enhance its durability.

The first embodiment, which has been described above, assumes that theshift position sensor 62 detects a gear shift by the transmission.However, an alternative gear shift detection method may be used. Forexample, a clutch sensor for detecting clutch engagement/disengagementmay be used to detect a gear shift upon clutch disengagement (in asituation where a manual transmission is used). Another alternativewould be to detect a gear shift in accordance with the ratio between theengine speed NE and vehicle velocity. Since a vehicle velocity sensor isgenerally installed in any vehicle, the use of a method based on vehiclevelocity makes it possible to detect a gear shift without adding a newsensor.

The first embodiment, which has been described above, disables theswitching operation in a situation where the operating state has changedfrom the single valve small lift region to the dual valve great liftregion under predefined conditions. However, the present invention mayalternatively disable the switching operation in a situation where theoperating state has conversely changed from the dual valve great liftregion to the single valve small lift region.

The first embodiment, which has been described above, uses a valvemechanism that continuously varies the valve opening amounts of thefirst and second intake valves 14L, 14R (in the dual valve variablecontrol mode) or the valve opening amount of the first intake valve 14L(in the single valve variable control mode). However, the presentinvention may alternatively use a valve mechanism that varies theabove-mentioned valve opening amounts in multiple steps.

The first embodiment, which has been described above, assumes that thepresent invention is applied to a variable valve operating apparatus foran intake valve. However, the present invention can also be applied to avariable valve operating apparatus for an exhaust valve.

The above modifications can also be applied to the other embodiments,which will be described later.

In the first embodiment, which has been described above, the singlevalve small lift region corresponds to the “single valve variablecontrol region” according to the first aspect of the present invention;the dual valve great lift region corresponds to the “dual valve variablecontrol region” according to the first aspect of the present invention;the arm coupling mechanism 72 corresponds to the “switching mechanism”according to the first aspect of the present invention; and the ECU 60corresponds to the “storage means” according to the first aspect of thepresent invention. The “normal control means” according to the firstaspect of the present invention is implemented when the ECU 60 causesthe arm coupling mechanism 72 to perform a switching operation inaccordance with the switching map; the “condition judgment means”according to the first aspect of the present invention is implementedwhen the ECU 60 performs steps 100 and 102; the “disable means”according to the first aspect of the present invention is implementedwhen the ECU 60 performs step 104; and the “enable means” according tothe fourth aspect of the present invention is implemented when the ECU60 performs step 106.

Second Embodiment Features of Second Embodiment

A second embodiment of the present invention will now be described withreference to FIG. 9. However, the differences between the foregoingembodiment and the second embodiment will be mainly described whileskipping the description of features common to these two embodiments ordescribing such features briefly. The system according to the secondembodiment can be implemented by using the same hardware configurationas the first embodiment and allowing the ECU 60 to execute a routineshown in FIG. 9, which will be described later.

While the vehicle is stopped, the driver may step on the acceleratorpedal to let the internal combustion engine 1 perform a freeacceleration (so-called racing) operation. This free accelerationoperation is rarely conducted for an extended period of time. Therefore,even if the operating state changes from the single valve small liftregion to the dual valve great lift region during a free accelerationoperation, it is anticipated that the operating state will revert to thesingle valve small lift region within a short period time. In view ofsuch circumstances, the present embodiment also refrains from switchingto the dual valve variable control mode in the above instance in orderto enhance the durability of the arm coupling mechanism 72.

Details of Process Performed by Second Embodiment

FIG. 9 is a flowchart illustrating a routine that the ECU 60 accordingto the present embodiment executes to implement the above functionality.First of all, the routine shown in FIG. 9 performs step 120 to judge inaccordance with an output generated from the shift position sensor 62whether the transmission is shifted to neutral (when a manual orautomatic transmission is used) or shifted to park (when an automatictransmission is used). If the transmission is not shifted to neutral orpark, the routine does not perform the following processing stepsbecause a free acceleration operation does not take place.

If it is found in step 120 that the transmission is shifted to neutralor park, the routine performs step 122 to judge whether the operatingstate of the internal combustion engine 1 has changed from the singlevalve small lift region to the dual valve great lift region. If thejudgment result obtained in step 122 indicates a change to the dualvalve great lift region, it can be concluded that a free accelerationoperation is being conducted. In this instance, therefore, step 124 isperformed to disable the switching operation of the arm couplingmechanism 72. More specifically, although the operating state of theinternal combustion engine 1 is changed to the dual valve great liftregion, the switching pin 74 is left inserted in the pin hole 76 torefrain from switching to the dual valve variable control mode.

Next, the routine shown in FIG. 9 performs step 126 to judge whether theoperating state has changed to a region other than the dual valve greatlift region, that is, to the single valve small lift region or dualvalve variable lift region. If the obtained judgment result indicates achange to a region other than the dual valve great lift region, it canbe concluded that the free acceleration operation is terminated.Therefore, the routine terminates to resume normal control (RETURN). If,on the other hand, the obtained judgment result does not indicate achange to a region other than the dual valve great lift region, it canbe concluded that the free acceleration operation is still beingconducted. In this instance, the routine returns to step 124 and keepsthe switching operation disabled.

When the above process is performed, it is possible to prevent the armcoupling mechanism 72 from performing an extra switching operationduring a free acceleration operation and enhance the durability of thearm coupling mechanism 72.

Third Embodiment Features of Third Embodiment

A third embodiment of the present invention will now be described withreference to FIG. 10. However, the differences between the foregoingembodiments and the third embodiment will be mainly described whileskipping the description of features common to these three embodimentsor describing such features briefly. The third embodiment has the samehardware configuration as the first embodiment. The system according tothe third embodiment can be implemented by allowing the ECU 60 toexecute a routine shown in FIG. 10, which will be described later, inaddition to the process according to the first or second embodiment.

As mentioned earlier, the arm coupling mechanism 72 moves the switchingpin 74 by using the hydraulic pressure of the lubricating oil for theinternal combustion engine 1. While the internal combustion engine 1operates, sludge (viscous material) may be produced in the lubricatingoil. If by any chance the switching pin 74 does not operate for anextended period of time while the sludge is deposited around theswitching pin 74, the switching pin 74 may bind in the hydraulic chamber75 or pin hole 76 and become inoperative.

As described earlier, the first and second embodiments disable theswitching operation of the arm coupling mechanism 72 in a predefinedsituation. This reduces the frequency with which the arm couplingmechanism 72 performs the switching operation. When the frequency of theswitching operation of the arm coupling mechanism 72 decreases, theswitching pin 74 is likely to stay put for an extended period of time.As a result, it is highly probable that the switching pin 74 may binddue to the sludge.

Therefore, if a predetermined value is exceeded by the number of timesthe switching operation of the arm coupling mechanism 72 was disabled orthe cumulative time during which the switching operation of the armcoupling mechanism 72 was disabled, the present embodiment enables theswitching operation to prevent the switching pin 74 from binding.

Details of Process Performed by Third Embodiment

FIG. 10 is a flowchart illustrating a routine that the ECU 60 accordingto the present embodiment executes to implement the above functionality.The routine shown in FIG. 10 is executed in conjunction with the routineshown in FIG. 8 or 9.

The routine shown in FIG. 10 performs step 130 to measure the number oftimes the switching operation of the arm coupling mechanism 72 wasdisabled by the routine shown in FIG. 8 or 9 and the cumulative timeduring which the switching operation of the arm coupling mechanism 72was disabled by the routine shown in FIG. 8 or 9, and store the measurednumber of times and cumulative time in the ECU 60. The routine thenperforms step 132 to judge whether predetermined values are exceededrespectively by the number of times or cumulative time. Thepredetermined values are based on the characteristics of the internalcombustion engine 1 and the vehicle in which the internal combustionengine 1 is mounted, and stored in the ECU 60. These values arepredetermined so as to ensure that the switching operation is performedbefore the switching pin 74 binds.

If the judgment result obtained in step 132 indicates that one of thepredetermined values is exceeded by the measured number of times orcumulative time, step 134 is performed to stop the routine's control fordisabling the switching operation, which is shown in FIG. 8 or 9, andresumes normal control. While normal control is exercised, the armcoupling mechanism 72 performs its switching operation in accordancewith the switching map.

Next, step 136 is performed to judge whether the switching operation hasbeen performed by the arm coupling mechanism 72 under normal control. Ifthe switching operation has been actually performed by the arm couplingmechanism 72, it means that the switching operation has been performedto prevent the switching pin 74 from binding. In this instance, step 138is performed to lift the ban on switching operation disable control bythe routine shown in FIG. 8 or 9 and enable a switching operationdisable control function. The measured number of times and cumulativetime, which were stored in step 130, are then reset to zero (0). In theabove process, whether the switching operation disable control functionshould be enabled is determined by checking whether the switchingoperation is actually performed by the arm coupling mechanism 72.However, an alternative determination method may be used. For example,whether the switching operation disable control function should beenabled may alternatively be determined by checking whether the armcoupling mechanism 72 is instructed to perform a switching operation.

When the above process is performed, it is possible to properly preventthe switching pin 74 from binding due to a decrease in the frequencywith which the arm coupling mechanism 72 performs a switching operationduring the process according to the first or second embodiment.

In the third embodiment, which has been described above, the“measurement means” according to the fifth aspect of the presentinvention is implemented when the ECU 60 performs step 130; and the“permission means” according to the fifth aspect of the presentinvention is implemented when the ECU 60 performs steps 132 and 134.

Fourth Embodiment Features of Fourth Embodiment

A fourth embodiment of the present invention will now be described withreference to FIG. 11. However, the differences between the foregoingembodiments and the fourth embodiment will be mainly described whileskipping the description of features common to these four embodiments ordescribing such features briefly. The fourth embodiment has the samehardware configuration as the first embodiment. Further, the fourthembodiment performs basically the same process as the first or secondembodiment.

FIG. 11 shows valve lift curves of the first intake valve 14L and thesecond intake valve 14R. The present embodiment assumes that the valvelift of the first intake valve 14L is substantially equal to that of thesecond intake valve 14R in the dual valve variable control mode. FIG. 11shows valve lifts A to E, which are described below.

Valve lift A is the maximum valve lift in the dual valve great liftregion (dual valve variable control mode). This valve lift is preset inaccordance with maximum power requirements for the internal combustionengine 1.

Valve lift B prevails in a state where the rotational position of thecontrol shaft 41 coincides with the pin switching position, that is, theswitching pin 74 aligns with the pin hole 76. More specifically, valvelift B prevails while the great lift arm 71 is not coupled to the secondswing cam arm 50R.

Valve lift C prevails in a state where the great lift arm 71 is coupledto the second swing cam arm 50R so that the valve opening amount of thesecond intake valve 14R remains large. More specifically, valve lift Cis the valve lift of the second intake valve 14R in the single valvevariable control mode.

Valve lift D is the minimum valve lift that can be set by the variablevalve mechanism 40. Valve lift E is the maximum valve lift that can beset by the variable valve mechanism 40. In the present embodiment, valvelift A represents the upper limit of its operating range; therefore,valve lift E is not actually used.

In the single valve small lift region, a target valve lift is set withina range from valve lift D to valve lift B. In other words, the targetposition of the control shaft 41 in the single valve small lift regionis within a range that begins at the pin switching position and extendstoward a smaller lift, smaller operating angle region. In the dual valvegreat lift region, on the other hand, the target valve lift is setwithin a range from valve lift B to valve lift A. In other words, thetarget position of the control shaft 41 in the dual valve great liftregion is within a range from the pin switching position correspondingto valve lift B to a position corresponding to valve lift A, which is ina greater lift, greater operating angle region.

As described above, the upper limit of the target valve lift in thesingle valve small lift region is represented by valve lift B. Whilenormal control is exercised, the single valve variable control mode,that is, a state where the great lift arm 71 is coupled to the secondswing cam arm 50R, is implemented in the single valve small lift region.Therefore, when the valve mechanism 18 is in the single valve variablecontrol mode, control is generally exercised while the range below valvelift B is defined as the target valve lift.

Meanwhile, the first and second embodiments may disable the function forswitching from the single valve variable control mode to the dual valvevariable control mode and stay in the single valve variable control modeas described earlier even when the operating state has changed from thesingle valve small lift region to the dual valve great lift region (step104 in FIG. 8 or step 124 in FIG. 9). Therefore, a target valve liftgreater than valve lift B may be set while the valve mechanism 18 is inthe single valve variable control mode. In this instance, the followingsituation occurs.

In the single valve variable control mode, the second intake cam 17usually drives the great lift arm 71, which then drives the second swingcam arm 50R via the switching pin 74, as described earlier. However, ifthe control shaft 41 rotates beyond the pin switching positioncorresponding to valve lift B and toward a great lift and largeoperating angle region in the single valve variable control mode, therange over which the first intake cam 16 swings the second swing cam arm50R becomes larger than the range over which the second intake cam 17swings the second swing cam arm 50R. This causes the second swing camarm 50R to reversely drive the great lift arm 71 via the switching pin74. In this instance, therefore, the input roller 73 for the great liftarm 71 leaves the second intake cam 17.

If the engine speed NE and load suddenly decrease in a situation wherethe input roller 73 for the great lift arm 71 is separated from thesecond intake cam 17 as described above, the control shaft 41instantaneously rotates toward a small lift and small operating angleregion. The input roller 73 for the great lift arm 71 may then come intocontact again (collide) with the second intake cam 17, therebygenerating noise or damaging the surfaces of the input roller 73 and thesecond intake cam 17.

To avoid the above problem, the present embodiment limits the targetvalve lift to valve lift B or smaller when a switch from the singlevalve variable control mode to the dual valve variable control mode isprohibited (step 104 in FIG. 8 or step 124 in FIG. 9), that is, when theoperating state enters the dual valve great lift region in the singlevalve variable control mode. This prevents the control shaft 41 fromrotating beyond the pin switching position corresponding to valve lift Band toward a great lift and large operating angle region while the valvemechanism 18 is in the single valve variable control mode. This makes itpossible to properly prevent the input roller 73 for the great lift arm71 from leaving the second intake cam 17. Consequently, the presentembodiment can absolutely avoid noise generation and prevent thesurfaces of the input roller 73 and the second intake cam 17 from beingdamaged.

In the present embodiment, the initial target valve lift in the dualvalve great lift region is within a range from valve lift B to valvelift A as described earlier. Therefore, if the target valve lift islimited to valve lift B or smaller in a situation where a switch fromthe single valve variable control mode to the dual valve variablecontrol mode is prohibited, the actual target valve lift is fixed atvalve lift B.

Since the present embodiment is the same as the first and secondembodiment except as described above, its further description is omittedhere.

In the fourth embodiment, which has been described above, the “valveopening amount limitation means” according to the sixth and seventhaspects of the present invention is implemented when the ECU 60 limitsthe target valve lift (target valve opening amount) to valve lift B orsmaller in a situation where a switch from the single valve variablecontrol mode to the dual valve variable control mode is prohibited (step104 in FIG. 8 or step 124 in FIG. 9). Further, the first intake valve 16corresponds to the “main cam” according to the seventh aspect of thepresent invention; the second intake valve 17 corresponds to the“sub-cam” according to the seventh aspect of the present invention; andthe input roller 73 for the great lift arm 71 corresponds to the “matingmember” according to the seventh aspect of the present invention.

1-7. (canceled)
 8. A variable valve operating apparatus comprising: avalve mechanism having a switching mechanism for switching between adual valve variable control mode in which the valve opening amounts of afirst valve and a second valve, which are provided for the same cylinderand of the same type, are varied continuously or in multiple steps and asingle valve variable control mode in which the valve opening amount ofthe first valve is varied continuously or in multiple steps with thevalve opening amount of the second valve fixed; storage means forstoring rules for dividing an operating region of an internal combustionengine into a dual valve variable control region, for which the dualvalve variable control mode should be selected, and a single valvevariable control region, for which the single valve variable controlmode should be selected; normal control means for causing the switchingmechanism to perform a switching operation in accordance with the rules;and disable means which, when the operating state of the internalcombustion engine is changed from the dual valve variable control regionto the single valve variable control region or vice versa within apredetermined period of time after a gear shift by a transmissionpositioned between the internal combustion engine and vehicle drivingwheels, avoids the switching operation by disabling the switchingoperation in anticipation that the operating state will revert to theprevious region within a short period of time.
 9. A variable valveoperating apparatus comprising: a valve mechanism having a switchingmechanism for switching between a dual valve variable control mode inwhich the valve opening amounts of a first valve and a second valve,which are provided for the same cylinder and of the same type, arevaried continuously or in multiple steps and a single valve variablecontrol mode in which the valve opening amount of the first valve isvaried continuously or in multiple steps with the valve opening amountof the second valve fixed; storage means for storing rules for dividingan operating region of an internal combustion engine into a dual valvevariable control region, for which the dual valve variable control modeshould be selected, and a single valve variable control region, forwhich the single valve variable control mode should be selected; normalcontrol means for causing the switching mechanism to perform a switchingoperation in accordance with the rules; condition judgment means forjudging, when the operating state of the internal combustion engineswitches from the dual valve variable control region to the single valvevariable control region or vice versa, whether a predefined condition isestablished for anticipating that the operating state will revert to theprevious region within a short period of time; disable means fordisabling the switching operation when the predefined condition isestablished; and enable means which, if the operating state of theinternal combustion engine does not revert to a previous region within apredetermined period of time after a switch from the dual valve variablecontrol region to the single valve variable control region or viceversa, enables the switching operation no matter whether the predefinedcondition is established.
 10. A variable valve operating apparatuscomprising: a valve mechanism having a switching mechanism for switchingbetween a dual valve variable control mode in which the valve openingamounts of a first valve and a second valve, which are provided for thesame cylinder and of the same type, are varied continuously or inmultiple steps and a single valve variable control mode in which thevalve opening amount of the first valve is varied continuously or inmultiple steps with the valve opening amount of the second valve fixed;storage means for storing rules for dividing an operating region of aninternal combustion engine into a dual valve variable control region,for which the dual valve variable control mode should be selected, and asingle valve variable control region, for which the single valvevariable control mode should be selected; normal control means forcausing the switching mechanism to perform a switching operation inaccordance with the rules; condition judgment means for judging, whenthe operating state of the internal combustion engine switches from thedual valve variable control region to the single valve variable controlregion or vice versa, whether a predefined condition is established foranticipating that the operating state will revert to the previous regionwithin a short period of time; disable means for disabling the switchingoperation when the predefined condition is established; measurementmeans for measuring the number of times the switching operation wasdisabled or the cumulative time during which the switching operation wasdisabled; and permission means which, when a predetermined value isexceeded by the number of times the switching operation was disabled orthe cumulative time during which the switching operation was disabled,permits the switching mechanism to perform a switching operation nomatter whether the predefined condition is established.
 11. A variablevalve operating apparatus comprising: a valve mechanism having aswitching mechanism for switching between a dual valve variable controlmode in which the valve opening amounts of a first valve and a secondvalve, which are provided for the same cylinder and of the same type,are varied continuously or in multiple steps and a single valve variablecontrol mode in which the valve opening amount of the first valve isvaried continuously or in multiple steps with the valve opening amountof the second valve fixed; storage means for storing rules for dividingan operating region of an internal combustion engine into a dual valvevariable control region, for which the dual valve variable control modeshould be selected, and a single valve variable control region, forwhich the single valve variable control mode should be selected; normalcontrol means for causing the switching mechanism to perform a switchingoperation in accordance with the rules; condition judgment means forjudging, when the operating state of the internal combustion engineswitches from the dual valve variable control region to the single valvevariable control region or vice versa, whether a predefined condition isestablished for anticipating that the operating state will revert to theprevious region within a short period of time; disable means fordisabling the switching operation when the predefined condition isestablished; and valve opening amount limitation means for limiting atarget valve opening amount when the switching operation is disabled bythe disable means.
 12. A variable valve operating apparatus comprising:a valve mechanism having a switching mechanism for switching between adual valve variable control mode in which the valve opening amounts of afirst valve and a second valve, which are provided for the same cylinderand of the same type, are varied continuously or in multiple steps and asingle valve variable control mode in which the valve opening amount ofthe first valve is varied continuously or in multiple steps with thevalve opening amount of the second valve fixed; a storage device forstoring rules for dividing an operating region of an internal combustionengine into a dual valve variable control region, for which the dualvalve variable control mode should be selected, and a single valvevariable control region, for which the single valve variable controlmode should be selected; a normal control device for causing theswitching mechanism to perform a switching operation in accordance withthe rules; and a disable device which, when the operating state of theinternal combustion engine is changed from the dual valve variablecontrol region to the single valve variable control region or vice versawithin a predetermined period of time after a gear shift by atransmission positioned between the internal combustion engine andvehicle driving wheels, avoids the switching operation by disabling theswitching operation in anticipation that the operating state will revertto the previous region within a short period of time.
 13. A variablevalve operating apparatus comprising: a valve mechanism having aswitching mechanism for switching between a dual valve variable controlmode in which the valve opening amounts of a first valve and a secondvalve, which are provided for the same cylinder and of the same type,are varied continuously or in multiple steps and a single valve variablecontrol mode in which the valve opening amount of the first valve isvaried continuously or in multiple steps with the valve opening amountof the second valve fixed; a storage device for storing rules fordividing an operating region of an internal combustion engine into adual valve variable control region, for which the dual valve variablecontrol mode should be selected, and a single valve variable controlregion, for which the single valve variable control mode should beselected; a normal control device for causing the switching mechanism toperform a switching operation in accordance with the rules; a conditionjudgment device for judging, when the operating state of the internalcombustion engine switches from the dual valve variable control regionto the single valve variable control region or vice versa, whether apredefined condition is established for anticipating that the operatingstate will revert to the previous region within a short period of time;a disable device for disabling the switching operation when thepredefined condition is established; and an enable device which, if theoperating state of the internal combustion engine does not revert to aprevious region within a predetermined period of time after a switchfrom the dual valve variable control region to the single valve variablecontrol region or vice versa, enables the switching operation no matterwhether the predefined condition is established.
 14. A variable valveoperating apparatus comprising: a valve mechanism having a switchingmechanism for switching between a dual valve variable control mode inwhich the valve opening amounts of a first valve and a second valve,which are provided for the same cylinder and of the same type, arevaried continuously or in multiple steps and a single valve variablecontrol mode in which the valve opening amount of the first valve isvaried continuously or in multiple steps with the valve opening amountof the second valve fixed; a storage device for storing rules fordividing an operating region of an internal combustion engine into adual valve variable control region, for which the dual valve variablecontrol mode should be selected, and a single valve variable controlregion, for which the single valve variable control mode should beselected; a normal control device for causing the switching mechanism toperform a switching operation in accordance with the rules; a conditionjudgment device for judging, when the operating state of the internalcombustion engine switches from the dual valve variable control regionto the single valve variable control region or vice versa, whether apredefined condition is established for anticipating that the operatingstate will revert to the previous region within a short period of time;a disable device for disabling the switching operation when thepredefined condition is established; a measurement device for measuringthe number of times the switching operation was disabled or thecumulative time during which the switching operation was disabled; and apermission device which, when a predetermined value is exceeded by thenumber of times the switching operation was disabled or the cumulativetime during which the switching operation was disabled, permits theswitching mechanism to perform a switching operation no matter whetherthe predefined condition is established.
 15. A variable valve operatingapparatus comprising: a valve mechanism having a switching mechanism forswitching between a dual valve variable control mode in which the valveopening amounts of a first valve and a second valve, which are providedfor the same cylinder and of the same type, are varied continuously orin multiple steps and a single valve variable control mode in which thevalve opening amount of the first valve is varied continuously or inmultiple steps with the valve opening amount of the second valve fixed;a storage device for storing rules for dividing an operating region ofan internal combustion engine into a dual valve variable control region,for which the dual valve variable control mode should be selected, and asingle valve variable control region, for which the single valvevariable control mode should be selected; a normal control device forcausing the switching mechanism to perform a switching operation inaccordance with the rules; a condition judgment device for judging, whenthe operating state of the internal combustion engine switches from thedual valve variable control region to the single valve variable controlregion or vice versa, whether a predefined condition is established foranticipating that the operating state will revert to the previous regionwithin a short period of time; a disable device for disabling theswitching operation when the predefined condition is established; and avalve opening amount limitation device for limiting a target valveopening amount when the switching operation is disabled by the disabledevice.